BAGHDAD — With political leaders deadlocked, Iraq’s parliament squabbled Monday over when to hold its next session, potentially delaying the formation of a new government for weeks despite the threat from extremists who have seized control of a large chunk of the country and declared the establishment of an Islamic state.

The acting speaker of parliament initially announced that the legislature would not meet again until mid-August because there was no agreement among factions over the top leadership posts — particularly the prime minister, with incumbent Nouri al-Maliki facing a campaign to replace him.

But after an uproar over the long delay, speaker Mahdi al-Hafidh announced Monday night that there was a preliminary agreement among lawmakers to meet Sunday, July 13. But even that appeared uncertain, since al-Hafidh added that an official announcement of the date would not come until Tuesday.

With politicians struggling to even agree on when to meet, it was hard to see how they could quickly forge a compromise on the much thornier issue of a new government. The impasse, coupled with the military’s sluggish counteroffensive, underlined just how difficult a task Iraqis face as they try to keep their country from fracturing along sectarian and ethnic lines.

The military suffered a new setback in its battle with the extremist advance Monday when the top commander of the armed forces battling militants in the west was killed by a mortar strike.

The United States, which withdrew the last American troops from Iraq in 2011, and other world powers have pressed for the quick formation of a new government, as has Iraq’s top Shiite cleric, the revered Ayatollah Ali al-Sistani. They are calling for an inclusive government that will draw support among Iraq’s Sunni minority away from the insurgency, led by a radical al-Qaida breakaway group called the Islamic State.

In Washington, White House spokesman Josh Earnest said the U.S. was disappointed that Iraq’s leaders haven’t moved more quickly to unify the country. He said difficult steps must be taken to solve the problem, but that “reaching those agreements and making those difficult decisions are necessary for Iraq to survive.”

Lawmakers met last week for the new parliament’s first session since April elections, but the meeting ended without agreeing on a new prime minister, president and speaker of parliament. The legislature had been expected to meet again Tuesday, but that session was called off since no progress had been made over the past week untangling the political situation.

The main point of contention right now is the post of prime minister, which holds most of the power in Iraq. Al-Maliki’s opponents — and many former allies — want him removed, accusing him of monopolizing power during his eight years in office and contributing to the current crisis by failing to promote reconciliation with Sunnis.

Al-Maliki, whose State of Law bloc won the largest share of seats in April’s election, has vowed he will not abandon his bid for a third consecutive term. But he didn’t win a majority in parliament and so needs allies to form a government.

An alliance grouping Shiite parties has yet to decide on its candidate for the job. The Sunnis and Kurds have refused, in turn, to present their respective nominees for speaker and president. Under an informal system that took root after the 2003 U.S.-led invasion that ousted Saddam Hussein, the prime minister’s job goes to a Shiite, the president’s post to a Kurd and the speaker of parliament’s chair to a Sunni.

Some of the stiffest criticism of al-Hafidh’s initial decision for an Aug. 12 parliament session came from the Shiite alliance, an umbrella group that includes al-Maliki’s State of Law bloc. It said the lengthy delay doesn’t serve the country’s interests, and it urged him to set a date no more than a week away — a demand that July 13 meets.

But Sunni lawmaker Dhafir al-Ani said it was the Shiite alliance that demanded the postponement due to difficulties within its ranks in settling on a candidate for prime minister.

There’s no guarantee that even with a new government Iraq can roll back the militants. The insurgent blitz has overrun most Sunni-majority areas of the country — including the second largest city Mosul — in a matter of weeks. But it has slowed since encountering stronger resistance in Shiite-dominated areas.

Last week, the group declared the establishment of a caliphate ruled by Shariah law in the land it controls in Iraq and neighboring Syria.

The Iraqi military launched an offensive aimed at recapturing the northern city of Tikrit, but the insurgents remain firmly in control of the city and have harried the army with roadside bombs.

Near Beiji north of Tikrit, government troops protecting the country’s largest oil refinery remain under siege.

Sabah al-Nuaman, the spokesman for counterterrorism services, said airstrikes hit a 60-vehicle insurgent convoy moving toward Beiji on Monday, destroying as many as 45 of them. The report could not be independently verified.

The government has also struggled for months to wrest back ground lost west of Baghdad in the Sunni-dominated province of Anbar.

On Monday, a mortar attack killed the commander of the Iraqi army’s 6th division, Maj. Gen. Najim Abdullah Ali, while he was overseeing a raid on the Anbar village of Karma, army spokesman Brig. Gen. Saad Maan Ibrahim said.

Al-Maliki lamented Ali’s death, calling him a “holy warrior” who was “martyred in the battlefield as he was fighting the terrorists.”

Sunni militants seized control of the city of Fallujah, near Karma, and parts of the Anbar provincial capital of Ramadi in January. The government has since reasserted its control of Ramadi, but Fallujah remains in insurgent hands.

In Baghdad, a suicide bomber rammed a vehicle packed with explosives into a checkpoint in the Shiite neighborhood of Kazimiyah, killing five policemen and three civilians, a police official said. He said 16 people were wounded.

A medical official confirmed the casualty figures.

Both officials spoke on condition of anonymity as they were not authorized to release information.

Associated Press writers Sinan Salaheddin in Baghdad, and Josh Lederman in Washington contributed to this report.